The C# editor in Visual Studio supports collapsing/expanding namespaces, classes and methods (aka the outlining feature). Unlike the C++ editor, it doesn’t allow to collapse blocks (everything with braces, such as if/else, using, switch, etc.). However, you can retrofit this feature with the C# Outline 2013 extension.
Navigate to Tools -> Extensions and Updates -> Ctrl + E -> Type “outline” -> Install extension and restart.
After restarting, blocks are outlined and you can collapse / expand them:
It also adds some new shortcuts: